Composition and solution properties of fluorinated block copolymers and their surface structures in the solid state

Toward Achieving Highly Ordered Fluorinated Surfaces of Spin-Coated Polymer Thin Films by Optimizing the Air/Liquid Interfacial Structure of the Casting Solutions

Thin polymer films with well-assembled fluorinated groups on their surfaces are not easily achieved via spin-coating film-fabrication methods because the solution solidifies very rapidly during spin-coating, which hinders the fluorinated moieties from segregating and organizing on the film surface. In this contribution, we have proposed a comprehensive strategy toward achieving well-ordered fluorinated thin films surfaces by optimizing the molecular organization at air/liquid interface of the film-formation solutions. To validate such a route, poly(methyl methacrylate) (PMMA) end-capped with several 2-perfluorooctylethyl methacrylate (FMA) units was employed as the model polymer for investigations. The air/solution interfacial structures were optimized by systematically changing the polymer chain structures and properties of the casting solvents. It was found that the polymers that form loosely associated aggregates (e.g., FMA₁- ec-PMMA₆₅- ec-FMA₁) and a solvent with better solubility to FMA while having not too low surface tension (i.e., toluene) can combine to produce solutions with well-assembled FMA at the interfaces. By spin-coating the solutions with well-organized interfaces, an ultrathin film with perfluorinated groups that were highly oriented toward the film surface was readily achieved, exhibiting surface energies as low as 7.2 mJ/m², which is among the lowest reported so far for the spin-coated thin films, and a very high F/C ratio (i.e., 0.98).

Influence of the linkage type between the polymer backbone and side groups on the surface segregation of methyl groups during film formation

Although poly(vinyl acetate) (PVAc) differs from poly(methyl acrylate) (PMA) only in the reversed position of the ester group, a large difference in the concentration dependence of the casting solution on the corresponding surface structure of the cast films of PVAc, PMA and poly(methyl methacrylate) (PMMA) was observed. The hydrophobicity of both PMA and PMMA films increased with increasing concentration of the corresponding polymer solution, whereas cast PVAc films showed the reverse trend. The surface structure of the cast films prepared with different concentrations of the casting solution, characterized by sum frequency generation (SFG) vibrational spectra, showed that the order of the methylene groups increased while that of the acetyl methyl group decreased on the surface of cast PVAc film with increasing concentration of casting solution. However, the order of the ester methyl group increased and that of methylene groups did not change for cast PMA films with increasing concentration of casting solution. The cast PMMA film showed a reverse trend compared with the corresponding PMA film. It is apparent that well-ordered ester or acetyl methyl groups on the surface, which are oriented away from the polymer film, rather than methylene groups, play an important role in determining surface hydrophobicity, as the latter shield the OC[double bond, length as m-dash]O groups of PVAc, PMA and PMMA film surfaces from being exposed, resulting in low surface free energy. The reason for this difference is attributed to the relatively low energy for ester methyl group reorientation, an ester group structure nearer to the trans state and more regular local configuration of segments in concentrated solutions of PMA and PMMA compared to that of PVAc.

Fabrication of polymer brush surfaces with highly-ordered perfluoroalkyl side groups at the brush end and their antibiofouling properties

The protein-resistant performance was enhanced greatly by constructing a polymer brush surface with perfectly close-packed perfluoroalkyl groups.

Protein-resistance performance enhanced by formation of highly-ordered perfluorinated alkyls on fluorinated polymer surfaces

In this paper, the relationship between the surface structure of fluorinated polymers and their protein-resistant property was studied by preparing films of poly(n-alkyl methacrylate) end-capped with 2-perfluorooctylethyl methacrylate (FMA) (PFMA(y)-ec-PnAMA(x)-ec-PFMA(y)) with various ordered structures of perfluorinated alkyls. These fluorinated polymers were synthesized via a controlled/living atom-transfer radical polymerization (ATRP) method. Both the surface free energy and the CF(3)/CF(2) ratio obtained by X-ray photoelectron spectroscopy (XPS) were employed to scale the ordered structures of the perfluorinated alkyls. Protein adsorption studies using fibrinogen as a test molecule were undertaken on the various films by XPS. The results show that the adsorbed mass of fibrinogen decreased linearly with increasing CF(3)/CF(2) ratio on the fluorinated polymer surfaces. When the CF(3)/CF(2) ratio reaches 0.26, there was almost no fibrinogen adsorption. This work not only demonstrates the design of a fluorinated copolymer film on glass substrate with desirable protein-resistant performance, but also provides a fundamental understanding of how the orientation of perfluoroalkyl side chains affects protein-resistant behavior on fluorinated surfaces.